ANKARA, Turkey — The Islamic State is the “primary focus” of Turkish investigators after the worst terrorist attack in the country’s history, Turkey’s prime minister said Monday, even as protests swelled over security measures before the deadly blasts.

The increasing signals of possible Islamic State links to Saturday’s bloodshed — which killed nearly 100 people — has raised pressure on Turkey’s government before elections Nov. 1 with critics demanding more steps to keep Syria’s civil war from spilling over into Turkey.

Turkey is a strong backer of rebels seeking to topple Syrian President Bashar al-Assad, but the nearly four-year civil war opened room for Islamic State militants to seize territory and possibly mount attacks in NATO-member Turkey.

There has been no claim of responsibility for the twin suicide blasts at a peace rally in the capital, Ankara, that claimed at least 97 lives and injured more than 500 people. Some political figures in Turkey say the death toll could be higher.

Turkey has opened one of its southern air bases for the U.S.-led coalition carrying out airstrikes on the Islamic State, raising fears of retaliatory

“If you consider the way the attack happened and the general trend of it, we have identified the Islamic State as the primary focus,” said Prime Minister Ahmet Davutoglu on Turkey’s NTV television, the Reuters news agency reported.

Davutoglu said investigators know how suicide bombers joined the rally, which was staged to call for an end to the long battles between Turkish forces and miniority Kurdish insurgents.

“We’re close to a name, which points to one group,” he said, without giving further details.

Tensions between Turkey’s government and the country’s more than 14­ million Kurds have flared in recent months, reigniting a decades-long struggle by ethnic Kurds to win autonomy from the Turkish state.

Turkish officials insist that there are no plans to postpone the general elections Nov. 1.

But anger has been directed at President Recep Tayyip Erdogan and others in the aftermath of the blasts, with some claiming security forces did not do enough to protect the rally.

“Thief, Murderer Erdogan” chanted mourners at one funeral in Istanbul, waving flags from the People’s Democratic Party, or HDP, a left-leaning, pro-Kurdish party that claims it was the target of the bombings.

Labor unions and lawyers’ groups also joined protests against the government in Istanbul and Ankara.

Saturday’s attack appears to bear similarities to a suicide bombing in July that killed more than 30 peace activists near the southern town of Suruc, which is on the border with Syria.